When oceanographers from Plymouth Marine Laboratory and the University of Rhode Island compared a large group of swirls, shown on the chart off the east coast of Iceland, with thermal images from an Earth observation satellite they found the swirls corresponded almost perfectly with the Iceland-Faroes Front - where the Gulf Stream meets cold waters coming down from the arctic.

The cartographer, Olaus Magnus, an exiled Swedish priest living in Italy, had a dislike of blank canvases and covered every available space with ink. But Professor Tom Rossby, from the University of Rhode Island, believes not every elaborate quill stroke was artistic licence.

’Their location, size and spacing seem too deliberate to be purely artistic expression. Nowhere else on the chart do these whorls appear in such a systematic fashion, ’

’They are the earliest known description of large scale eddies in the ocean - these are huge bodies of water, 100km in diameter, that turn slowly. It seems the lines were deliberately drawn to aid navigation.’

’We know mariners were aware of these fronts but they would not have the tools to quantify them nor the means to express them,’ he said.

The work, part funded by the Natural Environment Research Council, came about while Tom was discussing the Iceland-Faroes Front at a workshop in Bergen, Norway. Shortly afterwards Tom was reading ’Cod’, the international bestseller by Mark Kurlansky. The book contains an illustration of the Carta Marina.

’When I turned the page and saw the map I said, ’holy ---! These are identical to our satellite images!’ I don’t think I would ever have registered this had I not been in Bergen.’

Tom explained that in 1539 people did not understand the importance of some of the details in the map.

’The whorls in the map quickly lost significance. When the map was reissued in 1572 everything, including sea monsters, was faithfully reproduced, but the huge eddies had disappeared.’

The Carta Marina took 12 years to complete and contains an extraordinary amount of information. The list of towns’, lakes and regions is far more comprehensive than any map preceding it or following until well into the seventeenth century.

It is one of the first maps to give Finland and parts of Russia roughly correct proportions and it is the first map to fully portray the Baltic Sea, the Finnish Gulf and the Gulf of Bothnia in the north.

Northern Scotland, the Hebrides, Orkneys, Faroes and Greenland are described in detail, but so oddly is a non-existent island, Tile. This island may be related to the mythical northern community Thule. To the ancient Greeks, Thule was the northernmost habitable region of the world. Curiously, its location on the map puts it near St. Kilda in the Hebrides.

The oceans contain a similar richness of information. The map reveals details of shipping routes at the time and warns sailors of drift ice in the north - illustrated by a stranded polar bear on a floe. Whales, sea lions, walruses, crabs and lobsters are also depicted.

The giant sea snakes and other monsters are taken directly from the imagination of fishermen and sailors, though some researchers suggest these monsters may reflect commercial tensions at the time between the Hanseatic League* and England. It has also been noted that the monsters are only attacking vessels from countries that had joined the reformation.

Dr Peter Millar from the Remote Sensing Group at Plymouth Marine Laboratory became involved in the project when Tom needed accurate thermal information on the water temperatures in the region.

’There is always a great deal of cloud over the northeast Atlantic so it is difficult to get a clear image of the whole region. I merged images over the course of a month to get a complete picture. Things got exciting when I was able to provide Tom with an image of the eddy field. The data confirmed Tom’s theory that the swirls on the map were not artistic licence,’ said Peter.

Peter explained that the waters coming up from the south can be as much as five degrees warmer than the cold currents from the north. At the point they meet these huge eddies form. Sailors would have been aware of these large rotations of water as they affected navigation. When a heavy, slow moving craft sailed through the front its course would be affected by as much three points on the 32 point compass used at the time.

Peter said, ’They would notice a change in colour of the water too. Warm water from the south is a darker blue than cold water. The temperature difference means marine life will vary across the front and, right at the front, deep nutrient rich waters move up to the surface supporting phytoplankton and grazing zooplankton. This ready food supply brings pilot whales and other marine creatures to the area to feed.’

Tom has started a new investigation of these fronts working collaboratively with the Institute of Marine Research in Bergen.

’We want to know more about the currents and movements of these waters. We are laying down subsurface drifters that will be tracked acoustically. This is to see how waters get drawn into the region and organise themselves into the front. These floats will tell us how these waters spread out into the Greenland Sea and Norwegian Sea.’

Ancient Map of Africa Poses Questions

The unveiling in South Africa's parliament on Monday of a replica of an ancient Chinese map of the then known world which includes a recognisable outline of Africa is raising intriguing questions of which foreigners first explored the continent.

"The idea is to take us beyond what we have been ... brainwashed into believing" declared Speaker Frene Ginwala at the opening of the exhibition, which includes other maps and rock art.

The "Da Ming Hun Yi Tu", the Amalgamated Map of the Great Ming Empire, dates back to 1389, decades before the first European voyages to Africa.

Click and drag photo to resize.

Among recognisable features are the Nile River and South Africas Drakensberg mountain range.

The map also shows a great lake, covering almost half the continents land mass. Researchers suggest it may have been drawn on the basis of an Arab legend that stated "farther south from the Sahara Desert is a great lake, far greater than the Caspian Sea".

(The biggest lake in Africa, Lake Victoria, is in fact only a fifth of the size of the Caspian Sea.)

"We have the worlds best researchers working on it," said parliaments senior researcher Heindri Bailey, who was hesitant about drawing conclusions from it.

"Until we are able to gain the knowledge we wont speculate on it."

The original of the map is housed in Beijing where it has remained wrapped up, sealed and stowed behind a locked door since the fall of Chinas last emperor in 1924. Fewer than 20 people have had access to it since then.

The digitised reproduction of the map on silk is almost four metres (around 12 feet) high and more than four metres across.

Place names are written mostly in Manchu, a now virtually extinct language, and still in need to be translated.

Karen Harris of the historical and heritage studies department at the University of Pretoria said that as early as the 1st century AD records had been found in China mentioning places in Africa.

"They had the capability, definitely," she said. "Theres not so much evidence to prove it, but it isnt a closed book yet."

A picture dated 11 November 2002 shows a detail on the Da Ming Hun Yi Tu (the Amalgamated Map of the Great Ming Empire) dating back to 1389 which is arguably the oldest world map in existence that accurately reflects the African continent.

Harris said that at the time the Chinese were seeking tribute and not trade for the emperor and therefore would not have set up bases or left behind significant markings as was the case with Europeans.

This, she said, would make it difficult to uncover evidence in support of Chinese having been there, adding: "You wouldn't find human remains because the Chinese took their bodies back to their ancestral lands."

But Bailey said some circumstantial evidence existed in South Africa to suggest the Chinese had navigated around Africa long before Bartolomeu Dias rounded the Cape of Good Hope in 1488.

"Chinese pottery has been found in (South Africas northern) Limpopo Province dating back to around the 13th century and there's rock art in the Eastern Cape depicting Chinese-looking characters," Bailey said.

British amateur researcher Gavin Menzies, a submarine engineer, argues in "1421", a book which came out this month, that Chinese admiral Zheng He circumnavigated the globe between 1421 and 1423, 100 years before the crew of Portuguese explorer Ferdinand Magellan, who was killed en route.

Zheng He, a eunuch who never travelled with fewer than 300 ships, the biggest carrying 1000 people, is long known to have visited Asia, India, Gulf countries, and Somalia, from where he took back giraffes and lions.

The official history also mentions "Franca" (France and Portugal) and Holland, with the Hollanders described as tall people with red hair and beards.

To meet them in their homeland, Zheng He would have had to sail round the southern tip of Africa.

This is the first time that a copy of the map has been shown outside China. The original is a derivative of an even earlier one dated 1320, which was believed to have been destroyed.

That was before Zheng He's birth (he lived from 1371 to 1435), which deepens the mystery.

Some of the later European maps on show in parliament illustrate dragons, snakes and one-eyed monsters in the inland regions.